Antiphospholipid antibodies including the false-positive serologic test for syphilis, the lupus circulating anticoagulant, and the anticardiolipin antibody can be associated with recurrent thrombotic events, recurrent fetal loss, and thrombocytopenia. A range of other possible clinical associations also exists, including neurologic events, skin lesions, and cardiac lesions. The pathology of these lesions and the pathophysiology are discussed. Treatment is controversial but when indicated is directed toward prevention of recurrent episodes using anticoagulants including antiplatelet agents, warfarin, and heparin as well as occasionally prednisone with or without immunosuppressive agents.